He added that the velvety down feathers found elsewhere on owls' wings and legs absorb the remaining sound frequencies above 2,000 hertz, making owls completely silent to their prey.

"If the owl didn't have velvety feathers, the owl would be heard by the prey as the owl approached, and [the prey] would have time to scurry away," Lilley said.

Nixon, the raptor specialist, readily agrees that unique feather design gives owls the power of stealth flight. She also notes that the silence allows owls to more efficiently use their ears, which are positioned asymmetrically in their skulls: One ear is higher and more forward than the other, and each is shaped slightly different.

Human ears, by contrast, are shaped and positioned symmetrically on each side of our skulls.

But owls, because of their ears' asymmetry, hear sounds slightly differently through each ear. This allows the raptors to more accurately determine where a sound is coming from.

"This is often what really helps [owls to] pinpoint their prey," Nixon said, noting that the ability is sometimes more helpful to owls than night vision.

Quiet Aircraft

In aircraft design, noise reduction takes a backseat to fuel efficiency, Lockard said. The NASA research scientist notes, however, that the lessons learned from the study of owl feathers have the potential to increase where and how often planes can take off and land.

"Major airports like Chicago [O'Hare] and London Heathrow have requirements on the amount of noise per day an air carrier can generate. If you can reduce that, you can have more flights come in a day, which is important for these airlines," he said.

Incorporating owl-feather-inspired technology to dampen sound in aircraft requires that engineers clear a critical hurdle: coming up with a design that does not create extra drag when aircraft have reached cruising speeds and altitude.

Ideas under consideration include a retractable, brushlike fringe to mimic an owl's trailing feathers and a velvety coating on aircraft landing gear, Lilley said.

"The owl has been doing this silent flight for something like 20 million years. We are just now coming along and hope we might make use of some these ideas to get an airplane quiet within 20 years and even more quiet within 20 to 50 years," Lilley said.